Hybrid vehicles may include a motor and an engine to provide improved fuel economy as compared to a non-hybrid vehicle. The motor may assist the engine or operate separately from the engine to propel the vehicle. The vehicle's hydrocarbon fuel economy may be increased by stopping engine rotation and propelling the vehicle solely via the motor. Additionally, during some conditions, such as when the hybrid vehicle is stopped, it may be desirable to stop motor rotation to conserve electrical energy. Thus, there may be selected conditions when both the engine and the motor are stopped to conserve energy. However, stopping the motor and engine also stops torque converter impeller rotation which may increase a lag time between an increase in driver demand torque and producing noticeable torque at vehicle wheels. Therefore, it would be desirable to provide reduced lag in response to an increase in driver demand torque while still allowing the motor to stop for energy conservation purposes.
The inventors herein have recognized the above-mentioned disadvantages and have developed a driveline method, comprising: applying a torque via a driveline integrated starter/generator (DISG) to a torque converter impeller from a condition where DISG rotation is stopped in response to a driver demand torque greater that a first threshold and less than a second threshold, the torque at least thirty percent greater than the driver demand torque.
By supplying a torque that is greater than a driver demand based torque to a torque converter impeller, it may be possible to provide the technical result of reducing delay between an increase in driver demand torque and an increase in wheel torque. Further, electric machine or motor speed may be adjusted based on a compensation torque after the electric machine achieves a torque converter fluid force transfer speed so that wheel torque increases smoothly at a time when transmission pump output pressure is increasing. In this way, the torque converter impeller speed may be accelerated quickly to a speed where a transmission pump output pressure increases and torque transfer to the torque converter turbine begins. After reaching the torque converter fluid force transfer speed, the torque converter impeller speed may be adjusted to provide torque at the torque converter turbine that is related to the driver demand torque. As a result, accelerator tip-in (e.g., increasing accelerator pedal position) response may be improved by reducing torque delay so that the driver demand torque may be applied to vehicle wheels sooner.
The present description may provide several advantages. In particular, the approach may reduce wheel torque production delay in a driveline. Further, the approach may allow driver demand torque to be followed more closely. Further still, the approach may allow a vehicle to perform better after the vehicle's motor has stopped rotating to conserve electrical energy.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.